The present invention relates to solar cells. In particular, the invention relates to a method for restoring the efficiency of solar cells whose efficiency has degraded.
Within the past few years, large scale efforts have been made to manufacture photovoltaic solar cells in order that they may be used to produce power. In particular, one type of solar cell is the amorphous silicon solar cell of the type described in U.S. Pat. No. 4,064,521 entitled SEMICONDUCTOR DEVICE HAVING A BODY OF AMORPHOUS SILICON which issued to D. E. Carlson on Dec. 20, 1977; U.S. Pat. No. 4,142,195 entitled SCHOTTKY BARRIER SEMICONDUCTOR DEVICE AND METHOD OF MAKING SAME which issued to D. E. Carlson et al. on Feb. 27, 1979; U.S. Pat. No. 4,163,677 entitled SCHOTTKY BARRIER AMORPHOUS SILICON SOLAR CELL WITH THIN DOPED REGION ADJACENT METAL SCHOTTKY BARRIER which issued to D. E. Carlson et al. on Aug. 7, 1979; U.S. Pat. No. 4,196,438 entitled ARTICLE AND DEVICE HAVING AN AMORPHOUS SILICON CONTAINING A HALOGEN AND METHOD OF FABRICATION which issued to D. E. Carlson on Apr. 1, 1980; and U.S. Pat. No. 4,167,015 entitled CERMET LAYER FOR AMORPHOUS SILICON SOLAR CELLS which issued to J. J. Hanak on Sept. 4, 1979. Each of the foregoing U.S. patents is incorporated herein by reference.
Experience with the amorphous silicon solar cells of the type described in the foregoing U.S. patents has indicated that the efficiency of such cells will often degrade following a long exposure of the cells to light. In view of the fact that the intended application of solar cells involves their exposure to light, the degradation effect noted is an unfortunate one. Researchers in the field of manufacturing amorphous silicon solar cells theorize that the lack of cell stability and degradation results from a change in the intrinsic layer of the amorphous silicon body, which is typically comprised of a P-I-N or an N-I-P structure. The theory is that the degradation is caused by trapping or recombination of optically generated free carriers which results either from a decrease in carrier lifetime or from a field distortion affect resulting from a build-up of positive space charge in the intrinsic layer adjacent the N-layer of the cell. While the source of the degradation is not yet well known or understood, a method to eliminate the degradation would be desirable.